Niddah 7: Women With Irregular Cycles Who are Ritually Pure Until the Moment They See Blood

Today we learn a new Mishna regarding women who are without a veset kavu'a, a set menstrual cycle.  We already know that they cannot assume that their status as niddah begin when they sees blood.  Instead, they have to assume that anything they have touched within 24 hours since their last self-examination with be ritually impure.  However, there are four exceptions.  These women may not have a regular period, but they are still considered ritually pure until they actually see menstrual blood.  They are virgins, pregnant women, nursing women, and old women.

The Mishna Acharona teaches that because these women do not generally menstruate at all, the Sages need not worry that their vaginal walls were holding on to menstrual blood.  That would be an unusual situation, and the Sages do not set rabbinic decrees in unusual situations.  As well, these women have a well established chezkat tahara, presumption of purity, based on the fact that they do not usually menstruate.  

The Kehilat Ya’akov argues that most women are assumed to menstruate somewhat regularly, and thus her vaginal walls with hold back her blood at some point in her life, thus a more stringent set of laws regarding ritual purity are in order.  Again, we return to the principal that rabbinic decree is only required for a usual occurrence.